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A revolution using a cheap backflow concept

After I bought wrongly a set of 4 electric valves to be buried, and 1 anti-shipon electric valve to serve as a main line backflow prevention device I had to decide if I need to expend again more money to correct the situation, abort or redesign the concept. Well, being an engineer I accepted the challenge of redesign the concept.

First I have a manual valve from the main line, as an emergency shutdown, then I installed the anti siphon valve. The idea here is to avoid use sch 40 PVC piping after that by having an automatic main line shutdown. Then run a "just when required" main line and placed 4 individual normal valves, one for each of my zones. I know what you think, the antisiphone valve will not work as intended, but let me finish explain. I used 4 zones just because there is not enough pressure&flow to irrigate my front and back yard at the same time. Because is only grass and is always receiving approximately the same amount of sun I will not treat any zone with an special treatment.

Now, the tricky solution I made to let the main anti-siphon work as intended is by programing the timings.

Turn on the first valve

The next minute the main anti siphon valve will be turned on.

After the allowed time to irrigate the first zone, I will turn on the second valve.

One minute after that (I had to use minutes because system does not allow seconds) turn off the first valve and keep the second valve on for the desired time.

Exactly the same steps 3 and 4 until the 4th valve of my system is already turned on.

After the last zone or valve 4 worked the desired time, I turned off the main anti-siphon valve, allowing the release of the vacuum and preventing any back-flow.

A minute later I can close my valve # 4.

As you can see here I am avoiding to have water pressure on any of my buried pipes around my house so I don't have to worry for any leak there. And because of that I can afford to use a cheaper PVC pipe than the required for main line that is the Sch 40.

I am avoiding to buy several anti-siphon valves for each of my zones, with the expenses associated and with the advantage that I can have my valves buried.

Instead of buying an expensive PVB or other types of back flow preventative devices I just have one cheap valve with the anti-siphon feature. I am not injecting any chemical or anything so based on the code I am allowed to use Atmospheric vacuum break.

If you want to do something similar, please make sure you understand the concept that the AS (Anti Siphon) valve must be turned on after other valves are already opened, and must be the first one to be closed before closing the last valve. And always allow running flow when switching between zones in order to don't create any negative pressure to the AS valve.

If somebody with knowledge of how these stuff works have any feedback of any problem or weakness of my design, please comment to see how I can solve it.
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Well, forget about some portions of my original idea. I just was informed that the valves requires water pressure to work, so when openening the AS valve there could be a pressure back not allowing AS to work as intended. I may need to replace my AS valve with a normal valve and a PVB (Pressure Vacuum Breaker)

This post has been edited 1 times, last edit by "vallesj" (Jun 5th 2012, 11:53am)

None of what you posted has any relevance as far as plumbing codes are considered. Devices must provide absolute protection in and of themselves, without depending on any other devices or on human intervention. Since you seem to know what codes actually require, you now man up and do the job right, and find something that is not safety-related for your engineering flights of fancy.

vallesj,
If I understood everything then your idea would work in a physical sense.
Shows a lot of imagination.

Unfortunately, it misses out on some of the practical and code considerations.
If you are ever inspected I imagine the inspector would have a massive heart attack and you would have to hide the body somewhere.

ASV are pretty much the bottom of the barrel on backflows. They are cheap for a reason.
I would be very uncomfortable with your design. I'd probably bring bottled water to your house.

A PVB has a very high protection/price ratio. They don't cost much and the cheapest one is far better than what you have.

Consider this: wet_boots, wsommariva, hi.todd and me (myself? I? never could get the grammar right) are all professionals with a great deal of collective experience.
We are also pretty outspoken.
If we thought PVBs were a waste of money we would tell you.
They are not. Well worth your investment.

the real problem with "creative thinking" in plumbing, is that inspectors operate from a strict rulebook, and the idea of having a single atmospheric vacuum breaker upstream of any zone valves is a flat-out fail - you can even find some illustrated code books with this idea in an illustration, with a bar across it to indicate that you can't do it

at some point, homeowners might want to sell their houses, and they will find that their "creative plumbing" can render them unsaleable

Hey, I already edited my idea mentioning that I changed the AS valve with a PVB and a valve.. Actually $115USD more because I bought copper pipe to be overground. But still, I think is cheaper to have a main automatic valve and not use SCH 40 pipe after that rather than have always water pressure around the house. At least I am saving 15 bucks considering already the difference of cost of PVC SCH 40 and the cheaper SDR21 and the added valve.